Induction heating generally refers to the process of heating an object (usually a metal object) by exposing the object to a time-varying magnetic field and, thereby, inducing a current (e.g., an eddy current) in the object. The induced current creates heat. To create the time-varying magnetic field, an induction heating unit is used. An induction heating unit typically includes the following components: (1) a power unit for producing a radio frequency (RF) signal and (2) a load comprising a coil coupled to the power unit for receiving the RF signal and producing the time-varying magnetic field. The power unit may include: a rectifier (a.k.a., AC/DC converter) for converting alternating current (AC) to direct current (DC) and an inverter for converting the DC produced by the rectifier to an RF signal, thereby producing the RF signal provided to the coil.
In some applications it would be advantageous to couple the coil to multiple power units so that the coil receives an RF signal from the multiple power units. However, in such a system where the coil receives power from multiple power units, there is a need to ensure that the power units operate in unison.
SUMMARY
In one aspect there is provided a modular power supply system, which includes multiple power supply modules, for providing power to a common load. In some embodiments, the modular power supply system includes: a drive signal generator that generates a common PWM drive signal; a first power supply module configured to receive power from a first AC power supply source, the first power supply module comprising: (i) a first AC/DC converter for converting AC power to DC power, (ii) a first PWM control signal generator configured to generate a first PWM control signal, and (iii) a first switching system comprising a first set of switches and a second set of switches, wherein the switching system is configured to (a) receive the DC power, the common PWM drive signal and the first PWM control signal and (b) cycle the switches based on the common PWM drive signal and the first PWM control signal, thereby producing a first output signal for driving the common load; a first monitor for monitoring the output power or temperature of the first power supply module; a second power supply module configured to receive power from a second AC power supply source that is different than the first AC power supply source, the second power supply module comprising: (i) a second AC/DC converter for converting AC power to DC power, (ii) a second PWM control signal generator configured to generate a second PWM control signal, and (iii) a second switching system comprising a first set of switches and a second set of switches, wherein the switching system is configured to (a) receive the DC power, the common PWM drive signal and the second PWM control signal and (b) cycle the switches based on the common PWM drive signal and the second PWM control signal, thereby producing a second output signal for driving the common load; a second monitor for monitoring the output power or temperature of the second power supply module; and a master controller coupled to the first and second monitors, wherein the master controller is configured to (a) cause the first PWM control signal generator to modify the duty cycle of the first PWM control signal in response to the output power or temperature of the first power supply module exceeding a threshold and (b) cause the second PWM control signal generator to modify the duty cycle of the second PWM control signal in response to the output power or temperature of the second power supply module exceeding a threshold.
The modular system allow multiple power supply modules to combine their output power (usually RF output power) as a single system and deliver the combined power to the object to be heated using a common resonant circuit. The object to be heated and the common resonant circuit form the common load of the power system.
The above and other aspects and embodiments are described below with reference to the accompanying drawings.